army unit vs detachment

army unit and detachment both are nouns.

Word	Noun	Adjective	Verb	Adverb
army unit	Yes	No	No	No
detachment	Yes	No	No	No

As nouns, detachment is a hyponym of army unit; that is, detachment is a word with a more specific, narrower meaning than army unit:

army unit (noun)	detachment (noun)
a military unit that is part of an army	the act of releasing from an attachment or connection
	coming apart
	avoiding emotional involvement
	a small unit of troops of special composition
	the state of being isolated or detached